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If recipients that had generated a HB are included in a mailing, a message is not sent and HB is generated automatically, and added to the HB count for that account. Periodically, the system checks all recipients that have generated hard bounces and unsubscribes the ones that have 3 HB or more. The addresses will be unsubscribed permanently after the first hard bounce"
The reason why addresses are not immediately unsubscribed is that this allows the list administrator still find those recipients in the "Subscribed" group and in the list of recipients for a certain message. If the recipient were immediately unsubscribed, details on the error would not be visible.
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